Phosphorus-copper-antimony-tin brazing alloy

ABSTRACT

A phosphorus-copper based brazing alloy comprising by weight: 6.0% to 7.0% phosphorus; about 2% to about 8% tin; about 2% antimony; and the balance copper.  
     A process of using this alloy to produce a brazed joint with a raised shoulder and with little black oxide.

[0001] This is a continuation-in-part of co-pending U.S. patent application Ser. No. 09/913,000, filed Jul. 25, 2001.

BACKGROUND OF THE INVENTION

[0002] This invention relates to novel brazing filler metal compositions. Two families of alloys (phos-copper and phos-copper-silvers) are used to braze copper and its alloys. Silver brazing alloys (composed primarily of silver, copper, zinc, tin, nickel, manganese, and cadmium) are used to braze ferrous and non-ferrous metals and alloys. These brazing alloys are designed to work at low temperatures and to provide strong, ductile joints.

[0003] Researchers in the past have discovered that additions of other elements, such as tin and antimony, to phos-copper and phos-copper-silver, and nickel, manganese and lithium to silver brazing alloys, have increased the properties of these two families in important ways, adding strength to some and changing melting temperatures in others. For example, U.S. Pat. No. 5,066,456 discloses that the addition of tin and antimony up to six percent each to a phosphorus copper based alloy lowers brazing temperatures.

[0004] Applicant has discovered that an alloy containing by weight: 6.0% to 7.0% phosphorus, about 2% to about 8% tin, about 2% antimony; and the balance copper, produces a brazed joint with greatly improved and previously unexpected properties.

[0005] The first of such new and unexpected properties is that the alloy forms a large cap, or shoulder, during the brazing process, and does so at a temperature that has not been possible with phosphorus/copper brazing alloys in the past without the addition of silver to the composition of the alloys. In fact, these new alloys will form a cap or shoulder similar to or superior to a silver-containing phos/copper alloy and will do so at slightly lower liquidus temperatures than the silver-containing alloys. The liquidus temperatures of brazing alloys more closely represent the most important characteristic of where the alloy flows (the working temperature).

[0006] Air conditioning coils, heat exchangers, water coolers and other copper coils are manufactured by connecting copper tubing and fittings by brazing with copper-phosphorus or copper-phosphorus-silver brazing alloys. These alloys produce strong, ductile brazes, but the industry has long experienced a relatively high percentage of leaks after brazing. Most leaks are caught on the production floor during testing and are repaired. This double work of brazing and testing is very costly. More damaging, very tiny leaks can evade factory testing and end up as warranty work in the field that is both expensive and damaging to the company's brand image.

[0007] The phos/copper alloys now on the market all range within a solidus temperature of 1310° F. to a liquidus temperature of 1500° F. Alloys of even higher phosphorus content, up to 8%, are now in used to enhance productivity because of their lower operating temperature cost considerations. The non-silver alloys in this group are the most commonly used in industry and contain 7.1% to 7.4% phosphorus, the balance being copper. The fact that these alloys flow and join very well is problematic in that they also flow very thinly. Torch and furnace brazing is performed as rapidly as possible to achieve good productivity. While these alloys are quick to braze, they are difficult to observe for soundness. The entire 360° of the brazed joint must be carefully viewed by the operator, for it is here that a correction, if needed, should be made. These thin-flowing alloys produce only a very small cap, or shoulder, around the pipe at the fitting junction. The alloys are thin-flowing in that they flow like a heavy coating of paint, instead of more thickly as in a putty used to seal a {fraction (1/8)}″ crack).

[0008] Even a skilled brazer cannot tell 100% of the time that he has a totally leak-free connection by visually looking at his completed braze. In some places on a given braze connection, the brazing alloy can be seen to be in places as a shoulder between the two parts, while in other places the alloy drops in the adjoining area (the capillary) without forming any noticeable shoulder. When viewing this closely, the operator can often see that the joint appears to be 100% sound, but he can't be certain of it.

[0009] Most air conditioning companies submerge the copper coil, which comprises perhaps 100 brazes, into a water tank, and air pressure is added to this coil to determine if there are any leaks. The now-in-use phos/copper alloys, as described above, could be modified to form an advantageous cap by lowering the phosphorus content significantly. However, doing so is not feasible as the liquidus temperatures rise to a point of endangering the copper being brazed.

[0010] It is noteworthy that silver in the range of 6-15%, when added to the phosphorus/copper alloys described above, lowers the solidus temperature to 1190° F., allows the phosphorus contents to be reduced as much as 1.5%, allows the alloy to flow in a much thicker manner, and effects a noticeable cap or shoulder to the brazed area. The popular 15% silver-phos-copper alloy has the consistency of hot taffy when hot enough to braze, and easily forms a large cap or shoulder at the joint area. This visible fillet is quickly seen by the operator and any omission can be remedied. However, the addition of silver is quite expensive.

[0011] Another serious deterrent to being able to observe the quality of copper tubing brazed with phos-copper or phos-copper-silver brazing alloys is the formation of a black oxide that is formed on the actual braze surface and on the adjacent copper pipe. Because the braze and the copper pipe all turn black, it is difficult to closely inspect the actual braze.

SUMMARY OF THE INVENTION

[0012] A process of using a phosphorus/copper/antimony/tin brazing alloy to produce a brazed joint with a raised shoulder and with little black oxide, comprising the steps of:

[0013] a) melting an alloy comprising by weight:

[0014] 1. 6.0% to 7.0% phosphorus;

[0015] 2. about 2% to about 8% tin;

[0016] 3. about 2% antimony; and

[0017] 4. the balance copper;

[0018] b) applying the melted alloy to a joint to be brazed;

[0019] c) allowing the melted alloy to cool; and

[0020] d) forming a raised shoulder of solidified alloy about the joint without the substantial production of black oxide.

[0021] A principal object and advantage of the present invention is that it produces a substantial raised shoulder or cap about the brazed joint, which is a visible sign to the operator that the joint is sound.

[0022] Another principal object and advantage of the present invention is that it produces a brazed joint without significant black oxide, which can obscure the operator's view of the soundness of the joint.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023]FIG. 1 is an elevational view of a brazed copper joint that has been brazed with a phos-copper alloy of the prior art.

[0024]FIG. 2 is an elevational view of a brazed copper joint that has been brazed with a phos-copper-15% silver alloy of the prior art.

[0025]FIG. 3 is an elevational view of a brazed copper joint that has been braxed with an alloy of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0026]FIG. 1 shows a copper joint J that has been brazed with a phos-copper alloy of the prior art. Note the absence of any substantial shoulder about the brazed joint.

[0027]FIG. 2 shows a copper joint J that has been brazed with a phos-copper-15% silver alloy of the prior art. Although the joint has a substantial shoulder or cap S, there is also substantial black oxide O about the joint which obscures the operator's view of the soundness of the joint.

[0028]FIG. 3 shows a copper joint that has been brazed with an alloy of the present invention. A substantial cap or shoulder S is present, and, in addition, there is little or no black oxide present.

[0029] The alloy of the present invention preferably comprises: 6.0% to 7.0% phosphorus; about 2% to about 8% tin; about 2% antimony; and the balance copper.

[0030] Most preferably, the alloy comprises either 6.75% phosphorus and about 2% tin; or 6.7% phosphorus and about 6% tin.

[0031] The solidus temperature of the alloy is about 1178° F. and the liquidus temperature is about 1247° F.

[0032] The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof, and it is therefore desired that the present embodiment be considered in all respects as illustrative and not restrictive, reference being made to the appended claims rather than to the foregoing description to indicate the scope of the invention. 

What is claimed:
 1. A phosphorus-copper based alloy comprising by weight: a) 6.0% to 7.0% phosphorus; b) about 2% to about 8% tin; c) about 2% antimony; and d) the balance copper wherein the alloy produces a brazed joint with a substantial shoulder and without substantial black oxide.
 2. The phosphorus-copper based alloy of claim 1, wherein the percentage of phosphorus is 6.75%.
 3. The phosphorus-copper based alloy of claim 1, wherein the percentage of phosphorus is 6.7% and the percentage of tin is 6%.
 4. The phosphorus-copper based alloy of claim 1, wherein the solidus temperature is about 1178° F. and the liquidus temperature is about 1247° F.
 5. A process of using a phosphorus/copper/antimony/tin brazing alloy to produce a brazed joint with a raised shoulder and with little black oxide, comprising the steps of: a) melting an alloy comprising by weight:
 1. 6.0% to 7.0% phosphorus;
 2. about 2% to about 8% tin;
 3. about 2% antimony; and
 4. the balance copper; b) applying the melted alloy to a joint to be brazed; c) allowing the melted alloy to cool; and d) forming a raised shoulder of solidified alloy about the joint without the substantial production of black oxide.
 6. The process of claim 1, wherein the percentage of phosphorus is 6.75%.
 7. The process of claim 1, wherein the percentage of phosphorus is 6.7% and the percentage of tin is 6%.
 8. The process of claim 1, wherein the solidus temperature is about 1178° F. and the liquidus temperature is about 1247° F. 